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From: Tomas Elf <tomas.elf@intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, Intel-GFX@Lists.FreeDesktop.Org
Subject: Re: [PATCH 6/8] drm/i915: Use safe list iterators
Date: Fri, 09 Oct 2015 11:27:48 +0100	[thread overview]
Message-ID: <561796A4.4040907@intel.com> (raw)
In-Reply-To: <20151009074151.GX27939@nuc-i3427.alporthouse.com>

On 09/10/2015 08:41, Chris Wilson wrote:
> On Thu, Oct 08, 2015 at 07:31:38PM +0100, Tomas Elf wrote:
>> Error state capture is dependent on i915_gem_active_request() and
>> i915_gem_obj_is_pinned(). Since there is no synchronization between error state
>> capture and the driver state we at least need to use safe list iterators in
>> these functions to alleviate the problem of request/vma lists changing during
>> error state capture.
>
> Does not make it safe.
> -Chris
>

I know it doesn't make it safe, I didn't say this patch makes it safe.

Maybe I was unclear but I chose the word "alleviate" rather than "solve" 
to indicate that there are still problems but this change reduces the 
problem scope and makes crashes less likely to occur. I also used the 
formulation "at least" to indicate that we're not solving everything but 
we can do certain things to improve things somewhat.

The problems I've been seeing has been that the list state changes 
during iteration and that the error capture tries to read elements that 
are no longer part of the list - not that elements that the error 
capture code is dereferencing are deallocated by the driver or whatever. 
Using a safe iterator helps with that very particular problem. Or maybe 
I guess I've just been incredibly lucky for the last 2 months when I've 
been running this code as I've been able to get 12+ hours of stability 
during my tests instead of less than one hour in between crashes that 
was the case before I introduced these changes.

Thanks,
Tomas
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  reply	other threads:[~2015-10-09 10:27 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-08 18:31 [PATCH 0/8] Stability improvements to error state capture Tomas Elf
2015-10-08 18:31 ` [PATCH 1/8] drm/i915: Early exit from semaphore_waits_for for execlist mode Tomas Elf
2015-10-08 18:31 ` [PATCH 2/8] drm/i915: Migrate to safe iterators in error state capture Tomas Elf
2015-10-09  7:49   ` Chris Wilson
2015-10-09 11:38     ` Tomas Elf
2015-10-09  8:27   ` Daniel Vetter
2015-10-09 11:40     ` Tomas Elf
2015-10-13 11:37       ` Daniel Vetter
2015-10-13 11:47         ` Chris Wilson
2015-10-08 18:31 ` [PATCH 3/8] drm/i915: Cope with request list state change during " Tomas Elf
2015-10-09  7:48   ` Chris Wilson
2015-10-09 11:25     ` Tomas Elf
2015-10-13 11:39       ` Daniel Vetter
2015-10-14 11:46         ` Tomas Elf
2015-10-14 12:45           ` Daniel Vetter
2015-10-09  8:28   ` Daniel Vetter
2015-10-09 11:45     ` Tomas Elf
2015-10-13 11:40       ` Daniel Vetter
2015-10-08 18:31 ` [PATCH 4/8] drm/i915: NULL checking when capturing buffer objects " Tomas Elf
2015-10-09  7:49   ` Chris Wilson
2015-10-09 11:34     ` Tomas Elf
2015-10-09  8:32   ` Daniel Vetter
2015-10-09  8:47     ` Chris Wilson
2015-10-09 11:52       ` Tomas Elf
2015-10-09 11:45     ` Tomas Elf
2015-10-08 18:31 ` [PATCH 5/8] drm/i915: vma NULL pointer check Tomas Elf
2015-10-09  7:48   ` Chris Wilson
2015-10-09 11:30     ` Tomas Elf
2015-10-09 11:59       ` Chris Wilson
2015-10-13 11:43         ` Daniel Vetter
2015-10-09  8:33   ` Daniel Vetter
2015-10-09 11:46     ` Tomas Elf
2015-10-08 18:31 ` [PATCH 6/8] drm/i915: Use safe list iterators Tomas Elf
2015-10-09  7:41   ` Chris Wilson
2015-10-09 10:27     ` Tomas Elf [this message]
2015-10-09 10:38       ` Chris Wilson
2015-10-09 12:00         ` Tomas Elf
2015-10-08 18:31 ` [PATCH 7/8] drm/i915: Grab execlist spinlock to avoid post-reset concurrency issues Tomas Elf
2015-10-09  7:45   ` Chris Wilson
2015-10-09 10:28     ` Tomas Elf
2015-10-09  8:38   ` Daniel Vetter
2015-10-09  8:45     ` Chris Wilson
2015-10-13 11:46       ` Daniel Vetter
2015-10-13 11:45         ` Chris Wilson
2015-10-13 13:46           ` Daniel Vetter
2015-10-13 14:00             ` Chris Wilson
2015-10-19 15:32   ` [PATCH v2 " Tomas Elf
2015-10-22 16:49     ` Dave Gordon
2015-10-22 17:35       ` Daniel Vetter
2015-10-23  8:42     ` Tvrtko Ursulin
2015-10-23  8:59       ` Daniel Vetter
2015-10-23 11:02         ` Tomas Elf
2015-10-23 12:49           ` Dave Gordon
2015-10-23 13:08     ` [PATCH v3 " Tomas Elf
2015-10-23 14:53       ` Daniel, Thomas
2015-10-23 17:02     ` [PATCH] drm/i915: Update to post-reset execlist queue clean-up Tomas Elf
2015-12-01 11:46       ` Tvrtko Ursulin
2015-12-11 14:14         ` Dave Gordon
2015-12-11 16:40           ` Daniel Vetter
2015-12-14 10:21           ` Mika Kuoppala
2015-10-08 18:31 ` [PATCH 8/8] drm/i915: NULL check of unpin_work Tomas Elf
2015-10-09  7:46   ` Chris Wilson
2015-10-09  8:39     ` Daniel Vetter
2015-10-09 11:50       ` Tomas Elf
2015-10-09 10:30     ` Tomas Elf
2015-10-09 10:44       ` Chris Wilson
2015-10-09 12:06         ` Tomas Elf
2015-10-13 11:51           ` Daniel Vetter

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